1. Field of the Invention
The present invention is generally in the field of protective disconnect systems to terminate the transmission of RF power to cellular base station antennas mounted on power poles and other shared utility structures.
2. Description of the Related Art
The number of cellular telephones in the United States and in other countries is rapidly increasing. The increase in the number of cellular telephones in use has resulted in an increase in the number of cellular telephone base stations required to provide expanding coverage in previously unserved areas and to provide additional cells in many urban areas when the demand for cellular service exceeds the capacity of existing base stations. In general, a cellular base station comprises a mast, a tower or other support structure (e.g., a building) that supports one or more antennas a sufficient distance above the surface so that the antennas are able to transmit and receive signals over a geographic area, which defines a cell for the cellular network to which the antennas are coupled. A base station also includes one or more sets of transceivers, digital signals processors, control electronics, power sources and the like, which are generally positioned close to the support structure. The antennas on the support structure are coupled to the transceivers via radio frequency (RF) transmission lines. The cellular base stations are spaced apart by distances selected to provide overlap between the coverage areas of adjacent stations to enable ongoing calls to be handed over from one base station to the next when a mobile cellular telephone use moves between two coverage areas.
Although the support structures for many base stations are specifically constructed to support the base station antennas, in many areas, particularly urban areas, a site may not be available to erect a support structure for a base station. For example, an unused plot of land may not be available, the use of the available land may be restricted by ordinance, or the property owners in a desired location may not be willing to sell, lease or otherwise make the land available for a support structure.
In many cases where a suitable support structure cannot be erected or where it is not cost-effective to erect a support structure, cellular antennas are placed on existing support structures, such as utility poles carrying electrical power, telephone lines, or combinations of both. For example, an array of cellular antennas may be positioned on an electrical power pole or telephone pole above or below the existing power lines or telephone lines. The antennas may be attached directly to an unused portion of the pole or may be attached to an extension added to the pole for the purpose of supporting the antennas.
Although the RF energy radiated by the antennas of a cellular base station is not considered to be harmful to a person at ground level, the energy radiated is sufficiently great that a person should not be within a relatively short distance from active cellular antennas. Accordingly, a need exists to cease providing RF transmission signals to the cellular antennas when a utility worker ascends a shared utility pole to perform inspection, repair or maintenance of the lines or other utility equipment on the pole.